1. Field of the Invention
The present invention relates to an image reading apparatus for reading image information of a transparent original such as a photographic film and an illumination apparatus for use in such an apparatus.
2. Related Background Art
In the past, there has been an image reading apparatus that reads an image of a transparent original while illuminating the transparent original by a fixed surface light source as disclosed in Japanese Patent Application Laid-Open No. 1-101063. This image reading apparatus will be described with reference to FIGS. 10A and 10B.
FIG. 10A is a cross sectional showing the image reading apparatus, and FIG. 10B is a perspective view of the same apparatus. A light source for transparent originals 127 is disposed above an original table 121 of the image reading apparatus. At an end portion of a light guide plate 128, a rod-like fluorescent tube 129 is mounted. The fluorescent tube is disposed parallel to the original table 121 on which an original is to be placed. The light guide plate 128 is a light diffusion panel made of a resin. The light guide plate is so constructed that light incident on it from the fluorescent tube 129 is emitted from its original side surface uniformly.
The original table 121 is an original table on which a transparent original such as a photographic film is to be placed. A transparent original placed on the original table is held and fixed between the light guide plate 128 and the original table 121. A CCD is a linear image pickup element which is adapted to convert image information into an electric image signal. A rod lens array 123 is adapted to optically form an image of the transparent original on the CCD 122.
A carriage 124 on which the CCD 122 and the rod lens array 123 are mounted is adapted to be moved in the sub scanning direction along guides 125 and 126. The whole area of the transparent original is illuminated by the light guide plate 128, and image information on the transparent original is read by the CCD 123 through the rod lens array 123. The carriage 124 is moved along the sub scanning direction to read all the image on the transparent original.
Moreover, there has been an image reading apparatus that reads an image of a transparent original while illuminating the transparent original by a moving linear light source, as described in Japanese Patent Application Laid-Open No. 2003-087514. This image reading apparatus will be described with reference to FIGS. 11A and 11B. In FIG. 11A, reference numeral 136 designates an image sensor such as a CCD that functions as photoelectric conversion means to convert image information scanned into an electric signal. The image sensor is disposed in the main body 130 of the image reading apparatus. On the top of the apparatus main body 130, there is provided an original table 131. An original P placed on the surface of the original table 131 is scanned by an image scanning optical system 132 serving as scanning means to expose image information onto the aforementioned image sensor 136. In the image sensor 136, three rows of sensors on which red, green and blue filters are attached are provided to read the image on the original while separating colors. The aforementioned image scanning optical system 132 is composed of a lamp unit 133 and a mirror unite 134 that are moved parallel to the original table 131 for scanning and a lens 135 fixedly mounted in the interior of the apparatus main body 130. The lamp unit 133 is equipped with a white light source L1 and a first mirror M1 for reflecting reflection image light from the surface of the original P illuminated by the light source L1 toward the mirror unit 134. The mirror unit 134 is composed of a second and third mirrors M2 and M3 for turning back the image light having been reflected by the first mirror M1 toward the image sensor 136. In order to keep the optical path length constant all over the image reading area, the lamp unit 133 is moved at a speed twice as fast as the mirror unit 134. Accordingly, the scanning optical system having this type of structure is commonly called a 2:1 scanning optical system. These units are adapted to perform scanning (sub scanning) while powered by a drive source such as a pulse motor (not shown) in synchronization with a reading cycle of the image sensor 136. Reference numeral 137 designates a light source unit for reading transparent originals that serves as illumination means for reading transparent originals. Reference numeral L2 designates a light source disposed parallel to the light source L1 in the main body. Reference numeral 138 designates a semitransparent plate having a light diffusing function. The light source unit for reading transparent originals 137 can be opened/closed with a hinge 139 attached at the rear end of the image reading apparatus being the pivot.
When a transparent original is read, the light source L2 is driven by a drive source (not shown) to scan an area covering the original table 131 parallel to the semitransparent plate 138 in synchronization with the image scanning optical system 132 in the main body. During this process, the light source L1 in the main body is off. Light from the light source L2 is diffused in the semitransparent plate 138 to provide a distribution as shown in FIG. 11B on the surface of the original (FIG. 11B showing portion D1 in FIG. 11A in an enlarged manner). The light on the optical axis from the reading position of the main body of the image reading apparatus to the image sensor 136 is transmitted through the original placed at position P in FIG. 11A and guided to the image sensor 136.
Japanese Patent Application Laid-Open No. 2004-007547 discloses an image reading apparatus as shown in FIG. 12, in which a surface light source for illuminating an area corresponding to one frame of a film is placed manually by a user at the position of an image on a film on the image reading apparatus to read the image of the illuminated frame. In this image reading apparatus 140, a film holder having a slot having a width and a length corresponding to a transparent original 142 is placed on an original table 141, the transparent original 142 is set in the slot, and image reading is performed by scanning by an image reading portion 145 while the transparent original 142 is pressed by an illumination unit 144 for transparent originals from above.
Typically, a film is in the form of a strip including a plurality of consecutive frames, which has been cut from an exposed and developed roll film. According to the above-described method, a user is required to move the illumination unit for transparent originals 144 to another frame position to resume reading every time reading of one frame is completed. The frequency of the above-described operation increases with an increase in the number of the frames of the film to be read. This makes the operation troublesome.
On the other hand, an enlargement of the film reading area and an increase in reading speed are demanded by the market.
In the case of image reading apparatuses using a fixed surface light source, it is necessary to increase the number of lamps and light sources with an enlargement of the illumination area. This necessarily leads to an increase in the weight of the light guide unit itself, to an increase in power consumption and to an increase in the cost. Furthermore, an increase in the warm-up time will result from elongation of the lamp.
Moreover, in the case of image reading apparatuses using a liner, moving light source, with an increase in reading speed, a diving apparatus having a higher degree of accuracy is required for achieving synchronized movement of the light source and the image sensor.
Furthermore, in order to realize radiation with a high degree of uniformity while using point light sources such as LEDs, it is necessary to equip a large number of LEDs. For the above-mentioned reasons, the apparatus will become expensive and require a complicated control process.
In the case of image reading apparatuses using a surface light source for illuminating one frame of a film, it is necessary for the user to place it for each frame.
The present invention has been made in view of the above problems. An object of the present invention is to realize a user-friendly image reading process without requiring highly precise parts nor a highly accurate control process while restricting the peak of power consumption.